One way to save fuel in today's vehicles is the use of the so-called Automatic Start Stop function which turns off the engine each time the vehicle comes to a complete halt (such as at traffic lights) and restarts it automatically. Some relay functions in vehicles with start stop functions are impacted much more frequently than before, which places higher demands on reliability, control and diagnostics. Furthermore, very fast and high current for various sequences are required. The voltage levels of the vehicle electrical system may vary widely, which creates the risk of malfunctioning of the electronic system.
Patent application DE102010000656 describes a power supply system for a vehicle which uses two batteries. The power supply system for the vehicle has a first battery which supplies power to a starter, and a second battery with an internal resistance smaller than the first battery. A switch is arranged in a feed line between the first battery and the second battery. A power supply system control unit controls this switch. The power supply system control unit turns on the switch in the period for stopping an engine, turns off the switch element upon operating the starter, and turns on the switch element when the capacity of the second battery is less than a prescribed value during operation of an engine. In this way the electronic system is protected and always powered with sufficient power by means of the second battery. In the system of DE102010000656 both batteries are constantly charged and discharged, and this will negatively influence the lifetime of both batteries.
It is an object of the present disclosure to provide an alternative for the electrical power system described above wherein the second battery is less often used so as to increase its lifetime, which will decrease maintenance costs.